The coffee oil is then blended with other fuels to create B20 biofuel, which can be used in diesel buses without modification.

Oil giant Shell and United Kingdom start-up bio-bean have teamed up on a project to provide a low carbon biofuel for London buses that contains waste coffee grounds collected from high-street retailers.

London also creates enough coffee ground waste to generate a scale large enough to help fuel around a third of the London transport system. The company collects waste from high street coffee shops, as well as instant coffee factories, and uses it to extract an oil. The oil is used as a pure-blend for a 20% bio-component that is mixed with mineral diesel to form the B20 fuel.

Given the tiny proportion of coffee-based oil in the bus fuel, there was no immediate, empirical indication that the noisome whiff of central London's air would turn into the alluring aroma of, say, a Roman cafe, or even a Starbucks.

Bio-bean and its partner, Argent Energy, have also already claimed they have enough coffee oil in order to run one bus for an entire year.

In a first, waste coffee grounds will be used to make biofuels to power some of London's buses from today, according to a media report.

The founder of the company said: "It's a great example of what can be done when we start to reimagine waste as an untapped resource".

According to Bio-bean, Londoners create 200,000 tonnes of waste from coffee every year. Six-thousand litres of coffee oil have been produced so far.

Shell's collaboration with bio-bean and Argent Energy is part of Shell's #makethefuture energy relay, which supports entrepreneurs by turning energy innovations into a positive impact for communities worldwide.